1. Field of the Invention
The present invention relates to a liquid crystal composite material, and in particular relates to a liquid crystal composite material having an inorganic layered material.
2. Description of the Related Art
A switchable glass, also called a smart glass, is a particular kind of glass for decorating a building, wherein a liquid crystal layer is disposed inside the glass. The liquid crystal is used to alter light transmittance of the glass by electric voltage, such that the glass can be switched from being transparent to opaque. Recently, the switchable glass has been widely used in different sectors such as the office, building, hospital, housing, machine room, and aerospace sector. Also, switchable glass can be used as a projector screen.
The light transmittance of switchable glass is typically modulated by a polymer-dispersed liquid crystals therein. When an electrical field is applied, molecules of liquid crystal droplets rotate and align, such that the refractive indices of the liquid crystal and polymer match, permitting light to pass through the glass. When no electrical field is applied, the liquid crystals are arranged in random orientations, such that light is scattered, so that the switchable liquid crystal glass looks translucent.
Conventionally, the liquid crystal layer used in a switchable glass is a polymer-dispersed liquid crystal film (PDLC film). A problem with the conventional polymer-dispersed liquid crystal film is its poor light resistance, which results in poor opacity. In order to improve the contrast ratio of the polymer-dispersed liquid crystal film, an increase in film thickness is usually required. However, this increase in film thickness will also increase the driving voltage of the liquid crystals.
The refractive indices of the liquid crystal and the polymer must match to allow the PDLC film to become transparent when a voltage is applied. Therefore, the materials of the polymer and liquid crystals cannot be changed arbitrarily. Carbon-based inorganic compounds such as carbon tubes and carbon capsules, or layered materials are commonly used as additives to reduce the driving voltage of the device, instead of changing manufacturing processes. The above inorganic compounds may be TiO2, SiO2, or ZnO, for example. The layered material may be such as natural clay. In Taiwan patent application No. 200829664, a single layer of carbon nanotubes is proposed to improve the transmittance and reduce the electrical resistance thereof. However, the reduction of the driving voltage is still unsatisfactory, and therefore the applications of switchable glasses are still limited (for example, the driving voltage is still too high for implementation in the automobile industry.)
In addition, in Taiwan patent application No. 200630328; a conductive liquid crystal material is used to reduce the electrical resistance of the device. However, the polymers are required to be charged to accommodate the refraction index of the conductive liquid crystals. Likewise, if the polymers are replaced by conductive polymers, the liquid crystals also need to accommodate the refraction index of the polymers. Therefore, it is difficult to integrate this method into existing processes.
Thus, a novel method that can reduce the driving voltage of the polymer-dispersed liquid crystal device to broaden its applications without altering the existing process is required.